CONDENSATION OF VAPOR MIXTURES

Two substantial differences exist between the condensation of flowing vapour mixtures and pure vapours. Firstly, in the case of a mixture, t he compositions and thus the physical properties of both vapour and li quid phase change along the condensation path. secondly, the mass tran sfer in the vapour between phase determines in the most cases the whol e condensation kinetic. On the contrary, the condensation of pure vapo urs is controled only by heat transfer in the liquid phase, The presen t paper deals with the simultaneous heat and mass transfer processes d uring multicomponent condensation using the film model, The interactio n between the components and the mass transfer in the vapour phase are analysed on the basis of the Maxwell-Stefan-equations. In addition to the exact matrix solution of these equations, some of their approxima te solutions are also included into the considerations and compared wi th experiments. The results obtained with the film model are mostly in good agreement with experimental data, especially for simple flow geo metry, e.g. condensation in a vertical tube. The exact solution of the Maxwell-Stefan-equations leads to a better agreement between the calc ulations and the experiments than the simple approximate methods. The agreement is generally less satisfactory for complex flow configuratio ns as for example of a condensation in a horizontal shell-and-tube con denser with baffels. Here improvements seem to be necessary not only w ith regard to the interactions between the mixture components, but als o with regard to the calculations of binary mass transfer coefficients which are necessary for the use of the film model.